Indoor units (IDU) and outdoor units (ODU) are commonly used in wireless terrestrial and very small aperture terminal (VSAT) communication systems or networks. These VSAT systems are cost-effective communication networks that allow many smaller VSAT terminals to be geographically dispersed and located in many different areas, including rural and metropolitan areas. VSAT networks support internet, voice/fax, data, LAN and many other communication formats.
A VSAT network usually includes a large central earth station known as a central hub (or master earth station), a satellite transponder, and a large number of geographically disbursed, remote VSATs. The satellites are positioned in a geostationary orbit about 36,000 kilometers above the earth. A VSAT terminal receives and transmits signals via the satellite to other VSATs in the network. The term “very small” used in the VSAT name refers to the small antenna dish that typically is about 3 to about 6 feet in diameter and could be mounted in almost any location, such as a roof, building wall, or on the ground. The VSAT terminal has an outdoor unit (ODU) that includes an antenna, low noise blocker (LSB) in some instances, and a VSAT transceiver as part of the outdoor electronics and other components. The antenna usually includes an antenna reflector, feed horn and an antenna mount or frame. The outdoor electronics constitute part of the outdoor unit and include low noise amplifiers (LNA) and other transceiver components, such as a millimeter wave (MMW) transceiver.
The indoor unit (IDU) can be an interface, such as a desktop box or PC, that contains the electronics for interfacing and communicating with existing in-house equipment such as local area networks, servers, PCs and other equipment. The indoor unit is usually connected to the outdoor unit with a pair of cables, e.g., coaxial cable. Indoor units also include basic demodulators and modulators.
The use of millimeter wave (MMW) frequency bands allows wireless links to produce up to about an estimated 1,000 times the data capacity of digital subscriber loop (DSL) or cable modems, systems and offer a higher bandwidth and available at lower operating frequencies. Many terrestrial wireless systems are built using point-to-point, point-to-multipoint, local multipoint distribution services (LMDS), and mesh architectures. Each link end also contains the indoor unit and an outdoor unit. Commonly assigned U.S. published patent application no. 2003/0152140 to Antoniak, the disclosure which is hereby incorporated by reference in its entirety, discloses a new method and system of multiplexing complex digital data signals under the same cable as high frequency IF signals without interference. Telemetry control signals are transmitted and received with intermediate (IF) payload data and DC signals on a common cable between an indoor unit and an outdoor unit. A carrier signal can be modulated with telemetry control signals to represent serial data bits by switching ON and OFF a carrier tone for ON/OFF keying and forming a modulated signal.
In these systems that use indoor units and outdoor units, typically the transmit and receive data can be at an intermediate frequency and typically ranges from a few hundred MHz to few GHz. The telemetry tones are usually at much lower frequencies. In order for the indoor unit to communicate with the outdoor unit, a telemetry tone ranging from a few KHz to many MHz is required. Various types of modulation techniques have been used to code this telemetry signal stream. Some of the techniques include FSK (frequency shift keying) and OOK (ON/OFF keying), such as described in the incorporated by reference ′140 published patent application. In cases where a full duplex is required between the indoor unit and the outdoor unit, two (2) tones will be required. One tone is used to send telemetry data from the indoor unit to the outdoor unit and one tone is used for sending data from the outdoor unit to the indoor unit. In addition to the added cost of the circuitry required to generate these telemetry tones, spurs could be created at the output of the transmitter and receiver. These spurs are challenging and difficult to filter.